Offshore drilling operations require a blowout preventer connected with the drilling riser to control well pressure. A typical subsea blowout preventer (“BOP”) has many components, such as one or more annular blowout preventers, several pipe rams, connectors for connecting to wellhead equipment, and a quick release connector for releasing an upper portion of the BOP and the drilling riser from a lower portion in the event of an emergency. Most of these components, also referred to as functions, are hydraulically actuated.
The BOP has a control system, also referred to as a multiplex or MUX pod layout, to control these various functions by supplying hydraulic fluid pressure to perform the particular function. The control system has hydraulic valves, called SPM (sub plate manifold) valves, that supply hydraulic fluid pressure to the various BOP components. The control system has solenoid valves, that when receiving an electrical signal, send a hydraulic pilot signal to one of the hydraulic valves.
Several of the solenoid valves may be mounted in a solenoid valve housing that is filled with an electrically insulating dielectric liquid. A typical control system will have several solenoid valve housings. Each solenoid valve housing may have a pressure compensator to equalize the dielectric liquid pressure with the hydrostatic pressure of the sea water.
Current practice requires all of the solenoid housings to be drained of dielectric fluid any time a component located in one of the solenoid housings needs to be serviced. The total volume of dielectric fluid in the control system can exceed 80 gallons. As a result, a large quantity dielectric fluid is lost and must be replaced each time maintenance is required in one of the solenoid valve housings.